Rotary snap action mechanism



Sept 2, 3947. c. E; BUERKI ETAL ROTARY SNAP ACTION MECHANISM I Filed Dec. 10, 1945 2 Sheets-Sheet 1 I 78 3 I 77 @f 1% 76 I I b A x ms wherein the. necessity latchin wheel, to

of the latch wheel in.

Patented Sept. 2, 1947 ROTARY'SNAP ACTION MECHANISM.

Christian E. Buerki and N Milwaukee, Wis, assignors. to Cutler-Hammer in M lwa ee... W a corpor t o of De m- Ware Harold L. Mekelburg,

Apoli atinn December 0, .9. 5 Seria N 63 .115

7. Claims.

1 This invention relatesto a rotary snap action mechanism. Although, not limited thereto the mechanism i pa cularly Well adapted for eration of electric circuit controllersof the drum tyn An object of theinvention istoprovide arotary Snanaction mechanism which is unusually rugged and durable in construction and not likely-to get out of ord Another object is to providesuch a mechanism ual, operating member each position, thereof Another object is to in moving the drum from to another is eliminated. provide, a novel form of dyer h f anda associated therewith.

7 Another; object isto so. construct and arrange the a r of. paWlS a to ll fi lt e op ne its nexttion by the inactive pawl as an lookin of he latch wheel th ousht eedium 9 anassociated star wheel.

Another object. isto. provide for rotars move.- ment of adriven element from a given pesition to substantially any. desired number of other positions. by. merely increasing the number of notches in the latch wheel and by correspondingly increasing the number of projections .on the tar wheel.

Another object is to so construct and arrange the pair of pawls as to insure against locking of t e mechanism in any given rotary position air f. lo k gp s to be thereof in the event of breakage or other failure of the driving spring.

Another object is to provide novel'means for insuring return of each of the pawls to normal position after each operation ofthe snap action mech ism- Other objects, and advantages of the invention will hereinafter appear.

' The accompanying drawings illustrate a preferred embodiment of the invention which will now be, described, it being understood that the embpdiment. illustrated issusceptible of modi-fiication in respect of certain structural details thereof withinithe scope of the appended claims.

In the drawings: Figure 1 is afrarnentary horizontal sectional View of the fixed portion of a drum controller Casing, showing in top plan (and indotted lines) most .of the elements of our-improved rotary snap action mechanism; the polygonalgportiontof the driving shaft being shown in BC ZiQH- Fig, 2 is afragmentaliy: side?elevation-(viewed be r g d att h d to the.

for overtravel of the mane su c ed n u si incide 0 mas indicated by the arrows 2?} in Fig. 1) showing the construction and manner of pivotally suizportihgthe pair of latchingpawls.

Fig. 3 is a fragmentary vertical sectional view, on the line 3.-3 of Fig. 1; the casing cover, and bearing par-ts for both the driving and driven shafts being also illustrated, and

Fig, 4 is a. fragmentary top plan view, in separatdrelation, of the pawls shown inF-ig. 2; the pivo portion of the pin bei g shown transverse cross section.

Referring to Fig. 1 of the drawings, the numeral Ill designates the fixed portion (usually a metal casting) of a easing adapted to house or enclose a circuit controlling drum of any suit.-

.able or well known form having our improved sna ac pe a ing m chani m asso ia e therewith. Portion lg) pre ierably has perforated lugs H a d I ormed'in e ra y w th and proittine er ly rom t e: re ect ve s e ed es or t bottom a l 13' djacen th ea d of e latter; simi a p forat d lu (not shown) being also preferably: provided at the forward corners of said bottom wall. Said; lugs serve. the u ua purposev 0. providing ior attachmen of thevho using by bolts or rews to a floor or sime Alone ie e removable h usin member (ruptshown) of substantially U=shape in h n al o s s ction is adapted to fit betwee t e- 9 1 202 1 flangeor surface l4, l4 andthe cover portion l5; (see 3 any well known means being provided for attaching. said removable h using-memb to p tion l0- Cover portion L5 is. provided with. a relatively la e c rc l r open nsxlfi: (Fla 3) surrounded by an upstandin flan e I1, to. which a metal member I 8 is attached (preferably removably) b su tab emean ot w 8 '5: provided with a -Gent-rally located circular .I 9; surrounded by an upwardly extending *fiwg s Z9 andqa downwardly extending flange 2L. Fla go. 2;! is provided-with an annular recess 22, of; tangular iorm in transverse cross sec- P Q Z' PQ l Q -Jw. the lower. face thereof and commun ieating. with the opening l9. v Said-recess is idaptedito, accommodate a unit comprising a pair of annular metal members 23 and24-, the adjacent inner edges of which. are complemetally g eyed: to'provide a substantially semicircular.

io l-racefor partial accommodation of the usual serofballs 25. The other half of the ball-race isformed-by providing an 1 annular groove 26 of substantially semicircular form in the periphery oiia circular metal member 21 which is of a size to be freely-rotatable .within opening l9.

The members 23 and 24 are assembled with respect to member 21, with the balls 25 interposed therebetween; after which a relatively thin metal member 28 is formed thereabout as shown to retain said parts in assembled relation. Member 21 is provided witha centrallylocated opening 29 of poly onal form in transverse cross section (herein shown'as square) to accommodate with a rather close fit the upper end portion. Q r

35, of corresponding shape in transverse cross" section, of the driving shaft of the. device.

Said driving shaft is provided with a relatively slightly reduced cylindrical lower end portion 32; a shoulder 33 being thus provided between portions 3! and 32.

The driven shaft of the device is long intermediate cylindricalportion 3], and'a 1,

designated I by the numeral 34; on1y the upper end portion of; r

as of square form in transverse cross section, to

said shaft being illustrated. Shaft 34 is shown facilitate attachment of the ,usual segments or 5 contacts in a wellknown manner; it being understood that said shaft is of suficient length to accommodate the required or desired number of movable contacts (not shown) to afford the desired circuit controllingcharacteristics; the re- The dotted line rectangle 34* in Fig.3 is a gdiagrammatic representation of the drum composed contacts.

The'drive'n, or drum} shaft '34 is rotatably supported within the housing, in any suitable .manrie'r; the same preferably having ball type bearings at or adjacent the upper and lower ends'thereof; one of the bearings being shown'at 35 *in Fig. 3, and the same being substantially v quired number of stationary contacts on one or both sides of shaft 34 being likewise provided.

1 of the aforementionedstationary and movable like: the bearing unit (23, 24, 25, 21 28 for the upper end portion'sll of the driving shaft) aforedescribed. 'The' "metal? block associated with driven shaft 34 and forming a part of the bear ing 35 isdesignated by numeral '36.

' A'fnetal ratchet or latch wheel 31"havin'gan' integral hub 38' projecting downwardly therefrom has an opening 39 therethrough; said opening beingof square form in transverse cross section to slidably fit over the correspondingly shaped upper end of shaft 34e Hub-'38 is provided atone pointwith a threaded opening 40 to.accom-' modate the shank of a: set screw 4|, which wh'en tightened is adapted torigidly connect wheel 31 to shaft 35'; a split lock-washer 42*anda locknut .43Lpreferably being associated with set screw 41 .to' prevent accidental loosening thereofv In;

practice we prefer to providet'wo tapped openings 49 arranged at right angles to each other, and a corresponding number of set screws 4|.

-Latch wheel 31 is providedin itsupper surface with'a-centrally: located countersinkor recess 44 110, providel'a seat for' the ball-bearing unit of known form, consisting of complementary outer elements 45 and 46, an inner element 41, and the usual set of balls 48. Thereduced'lower end 32' of the driving shaft fitswithin the' circular opening in the-inner element 41; the aforementioned shoulder, 33 being adapted to-seat againstthe upper surface of element 41"(Fig. 3) L A latch-trippingg(or pawl-tripping) star-wheel 49surrounds the lower. end of the intermediate cylindrical portio 3| of the driw'ng' shaft; a tubular member. 501 composed of; self-lubricating hearing material beingpreferably interposed between. wheel49and saiddriving shaft; Wheel 49 as shown overlies the aforementioned elements 45 and 41 of the ball-bearing unit to retain the latter in proper position. 7

A transversely divided metal spool composed of like upper and lower portions 52, 52 has said portions strung upon the intermediate cylindricalportion 37!..of the driving shaft; said portions being adapted to jointly accommodate a multiplecoil torsion spring 53, "the outwardly extending end portions of which are designated by numerals 54 and 55. Spool portions 52, 52 are interposed: "1 between the hub5l of wheel 49 and a metal block 56 having a square opening 51 therethrough to accommodate thelower end portion of the correspondingly shaped portion 3 0 of the drivin a has been pressed into the opening 59, as shown in Fig. 3, said parts are preferably tack welded to each other at the peripheral line designated by numeral 6| in Figs. 1 and 3.

A-second, but somewhat'longer, pin 52 is provided; the same having a press fit within an opening 63 extending through the aforementioned wheel 31 and projecting upwardly, from the latter, as best illustrated'in Fig. 3. Pin 62] r is likewise preferably tack welded to wheel 31 along the peripheral line designated'by numeral 64 (Fig. 3). As shown'in Figs'. land 3 both of the pins 69 and 52 are overlapped by the spring ends 54and 55 on opposite sidesthereof, respectively. As shown in Figs. 1'and3, wheel 49 is provided with an arcuate slot 65 to aiford cleareralcontours'of the respective wheels .49 and 31 is best illustrated in Fig. 1. v the latch wheel 31 is shown as having six peripheral notches 31 31 31, 31 31 and 31? The. portions of saidnotches hidden from view by wheel'49 are indicated by dash lines in Fig. 1.

The latch-release or star wheel 49 is provided with six double-inclined cam projectionsrespectively designated 48*, 49*, 49, 49 49 and 49,,

Like relatively short pins 65 andfifi (preferably' of cylindrical form) are rigidlyfattached to the l respective projections 49 and 49% and project the lower end ofp'in 69, according to the direction'of-rotation of driving'shaft 39, "asby means I of the usual manual operating handle" Knot shown) In practice we preferto provide the pro.-

-jections 59 and M -with circular openingsto accommodate reduced portions or shanks formed on pins 55 and 66 the ends of whichshanks' are 'upset over the. lower surface ofwheel'49,' as

shown at fifi in'Fig. 3. r A bracket 61 "has a horizontalportion I51 attached to the lower surface, of cover member l5 in any suitable manner, as by means of a pairof bolts '58, 58' and nuts 58*, 59 a downwardly off set horizontal portion .91 of said bracket having an opening iil to accommodateithei upper reduced 'end--portio'n '69 of-a, pivot p'injv said end portion 'ance between the same andpin 62." The periphupwardly-therefrom for selective engagement by in upset asishown at f59 (Fig. 3) to "secure th'epin to said bracket, The relatively arge intermedialte portion 59 ofsaidpinis surrounded bythe coils of: a torsion spring 10 whose'endpfor- V V tions or extensions 19 and 19 are normally biased into engagement with oppositesid'es re- '75Qspectively'of a pair ofstuds orlpins Hand 12; Q

the pin 1 Iv having a Shank portion riveted to, the aforementioned bracket portionfil a shown at H (Figs. 1 and 3)., and the pin [2 having a shank riveted. to the lower surface of a metal plate 13, as Shown at '12 in Fig, 3. Plate 13 is rigidly and permanently attached, as by fusion W l ing, than-upper machined metal member M, which is preferably of. square form in transverse cross section. as illustrated. in Fig. 4; three-fourths of the lower surface area thereof being cut away, or offset upwardly to provide a substantially triangular projection Or stop portion, as indicated in dotted lines at M in. Fig. 4. A second metal member 74 (of the sameform as that aforedescribed) is shown at the right-hand side of Fig. 4, said second member bein reversed end- Wise,. so that the. projection 14F is adapted to cooperate. with the first member to limit clockwise movement of the upper member M and counterclockwise movement of the lower member M. The members M having openings 14 therethrough to freely accommodate a tubular bearin member formed of a suitable bearin metal or alloy. Bearing member 75*. is freely slidable onto the reduced pivot portion. 59 of the aforementioned pin; said pivot portion iill having. a transverse opening therethrough adjacent its lower end to accommodate a cotter pin 15 or the like, whereby members '54, M and l5 are held in assembled relation thereto. A pair of metal pawls l7 and '18 (which may be bent in reverse directions as illustrated from identical blanks) have portions 77 and 18*, respectively, of reduced with fusion welded or otherwise rigidly attached to members "id in the relative positions shown in Figs. 1 to 4. The latching end portions N and T8 of pawls ll and 78 have opposite faces located in parallel planes approximately radial to the axial center ofdriven shaft said end portions preferably having double-inclined edge portions designated by numerals Ti and 18 (Fig. 1).

A pair of like sheet metal members have portions 759 and 53* thereof spot-welded or otherwise rigidly attached to the adjacent portions li and 78 of pawls El and 18; the aforementioned members having integral portions 79. and 33 bent as shown to lie in substantially parallel planes in the normal postions of the parts, as shown in Fig. l. Portions. l9? andSD are pref erably provided with cylindrical bosses 79 and 559, Figs, 1 3 and 4, which act to center and retainthe opposite ends of a relatively heavy. coiled compression sprin 8!, whereby the pawls Tl and i 8 are biased to the normal positions thereof shown in Fig. 1 The spring 8! is adapted to provide for movement of either ofv the pawls T! or 78 relatively to the other in the event of breakage or other failure of the main torsion spring 53, to thereby insure against looking or binding of said pawls with respect to the wheels 37 and49 of thesnap action mechanism, as hereinafter more fully described. 7 Y

' As shown in Fig. 3, the ball bearing associated with the upperend portion of driven shaft 34 is supported by a bracket member 82, which may be attached in any suitable manner to the part is cfithe drum housing. Bracket '82 is provided with an opening 82% to provide rotary clearance forthepart 3;6 of said bearing. The metal shell .83 which retains the outer elements of the bearing in assembled. relationship, to each other, is preferably weldedor otherwise rigidly attached t e' lfr nd es; a or a n lus wh h is inte r d t ach d t b ack t 82. AS shown in s; and m mbe .56 and norenergy in the latter.

t on of. the riving ha t. are p ovided with openings extending transversely therethrough to accommodate with a drive fit a tapered pin 85, whereby member 56 is restrained against mQVee ment axially of thedriving shaft.

With the parts of the snap action mechanism constructed and arranged as aforedescribed, the driving shaft 30 may be rotated continuously in either direction to provide for snap movement of the driven shaft (and the movable dr m, ontacts or segments carried thereby) through a total range of twelve different positions spaced thirty degrees apart. In practice, at least one of. said positions will be an off position of the drum. If it isv desired to limit rotary movement of the drum in opposite directions through a maximum range of eleven different positions, a suitable. stop member such as that shown in dotted lines at in Fig. 1 may be rigidly attached to a part (such as block 56) which is rotatable with the driving shaft 30; stop 86 being adapted to cooperate with a suitable stop such as that shown in dotted lines at 8'! in Fig. 1.

Stop 87 is preferably rigidly attached to the stationary part It! of the drum housing, asillustrated. With suchan arrangement the drum cylinder, represented; by driven shaft 34., may be rotated with a snap'action to eleven different positions spaced thirty degrees apart. Thusif it be assumed that the stationary and movabl contacts of the drum are arranged to provide for off, positioning of the drum parts in the respective positions of the parts of the snap action mechanism shown in Fig. 1, then upon clockwise rotation of driving shaft 393 the drum parts may be made to assume in sequence ten other rotary positions, all of which may be on positions to provide for commutation of a circuit to be controlled, or any number of which may likewise be 01?, or circuit interrupting, positions.

By suitably widening stop member 87, or byadd ing a second stationary stop member such as that shown in dotted lines at 88 in Fig. l, the total number of different rotary positions to which the drum cylinder may be moved in sequence with a snap action is reduced to ten.

If the drum is ofthe reversing type, the parts as illustrated may be assumed to be in off Dosi tion, and stops such as those shown atBI and 88 may be properly positioned to provide formovement of the drum cylinder with a snap action in either direction to five (or less than five) different on positions; it bein obvious that the drum would be required to be returned to said off position before being rotated in a direction to provide the reverse connections afforded by such drum. The stationary andmovable contacts of thedrum and the stop members may be arranged in various different ways commonto the drum controller art, dependingupon the particular circuit controlling functions desired.

The operation of the snap action mechanism is as follows: Assuming the drum parts to be in off position, upon clockwise movement of driving shaft 311, as by means of a suitable manually operable handle attached thereto, the pin Gil will move the projecting end 55 of torsion spring 53 to store Theend 54 of said spring will tend to move. with pin 60, but will be restrained by engagement thereof with pin 62, which is attached to the latch wheel 3'! the latter bein locked against clockwise rotation by ongagement of the lower shoulder of notch 37 (Fig.

1)., which isinitially quite closely adjacentthere-fl to, with thelatchingendrportion Til. ofpawll].

7 Pin 60 continues in a clockwise direction until it engages the-relatively short pin 66* on star Wheel 49,. whereupon the latter is likewise positively driven'in a clockwise direction. Such clockwise movement of wheel 49' results in engagement of the left-hand inclined edge orcam'su'rface of projection 49 with the end 11 of pawl 11 to rotate the latter out of the notch 31 When pawl 11 has been rotated sufficiently to provide clearance for the outer edge of the portion 31 interposed between notches 31 and 31 the wheel 31 will move with a snap-action, under the bias afforded by spring 53, until the righthand shoulder of notch 31 is engaged with the other pawl 18, as indicated by the dotted line notches 31 and 319 in Fig. 1. It is to be understood that during the aforementioned rotating or notch 31, but with the right-hand shoulder of the latter adjacent said pawl, as' indicated in dotted lines in Fig. 1), and upon lifting of pawl 18 until it clears'the outer edge of portion 31 (located between notches 31 and 31) the wheel 31 will again be moved clockwise with a snap action until the right-hand shoulder of notch 31 (note dotted line showing of portion 31 in Fig. 1) engages the pawl 11, whose end is then positioned within notch 31 The aforementioned lifting of pawl 18 acts in the manner aforedescribed to temporarily tilt pawl 11 inwardly against the normal bias of spring 18, for the purpose aforedescribed.

Inasmuch as the driven shaft 34 is rigidly connected with wheel S'l'it follows that snap moveaction of driving shaft cylinder carried thereby) by the cooperative 30,'pins 60 and 62, pin 66 or 6B, and slot 65., either end wall of which is adapted to engage and positively drive pin 62 in the event of breakage of spring 53.

The aforedescribed arrangement of parts is such that upon rotation of the driving shaft 30 '15 position of the portion 31 interposed between releasing movement 'of pawl 11 the pawl 18 will 7 in eitherdirection from a given position to the next succeeding operative position the driven shaft will be moved with a snap action to a rotary position substantially exactly thereto. That isto say, no overtravel of the driving shaft is required to effect snap movement of the driven shaft to the position selectedtherefor by manual positioning of the usual operating handle, This feature is of great practical importance, especially when an indicating dial or legends are employed in conjunction with the manual operating means; obvious that if the handle of the driving'shaft is manually released prior to complete movement thereof to its next succeeding rotary position, the

. torsion spring 53 will act automatically to effect return of said driving shaft to its last preceding position. 'Correct indication of the condition of' 1 the circuit or circuits controlled by the drum is therefore insured under all conditions.

We claim:

1. In an operating mechanism for a circuit controller, in combination, rotatable driving and driven shafts, a coiled torsion spring forming a driving connection between said shafts, means for effecting rotation of said driven shaft with a snap action from any one of a plurality of positions thereof to another, said last mentioned.

means comprising a latch wheel rigidly attached to said driven shaft and a pair of spring-biased pawls selectively cooperable with said latch wheel to temporarily lock the same pending storage of a given amount of energy in said torsion spring, a star wheel carried by said driving shaft and with respect to which the latter has a predetermined degree of lost motion upon rotation of 7 said driving shaft in either direction, said star ment of the drum t l to each of its various posi- -is ofisuch'size or caliberas to afford the necessary torque or power.

Clockwise rotation of driving shaft '36 may:

wheel coacting with each pawl when active to effect disengagement thereof from'sa'id latch wheel to effect snap movement of said driven shaft to another'rotary position under'the im- 7 pulse of said torsion spring.

2. In an electric circuit controller, in'combination, a rotatable driving shaft {and a rotatable thus be continuedthrough one onmore complete revolutions thereof (in the absence of any stops such as 86, 81) and. as will be apparent, the snap action mechanism acts in a substantially similar manner (but in reverse relationship to the parts of wheels 31 and 49). upon coutnerclockwise rotation of driving shaft 38. h I

As will be apparent from the foregoing description, the spring 53 acts 'tdbias wheel 49 to the normal position relatively to wheel 31 and rela- 'tively to block 56 .as shown in fulllines'in Fig. 1.

Coiled torsion spring 18 acts to bias pawls 11' r and 18 to the normal positions theieof relatively to each other and to given normal positions with a'foredescribedfto permit yieldable movement of either pawl 11 M18 relatively to the other to 53.: By this means we insure the ability 't ofposi tively rotate the driven shaft (and the'druin respect to theperipheries of wheels}? and 39. v Coiled compression spring 3! acts in the manner driven'shaft, a coiled torsion spring affording a drivingconnection therebetween, alatch wheel rigidly attached to said driven shaft, a star wheel a loosely. mounted on said driving shaft adjacent and in parallel relationship to said latch wheel,

means including a pin'associated with said driving shaft and said spring to positively limit "the degree of rotation of said driving shaft in either direction independently of said star wheel, .a

pair of spring-pressed' pawls arranged to be see I lectively engaged by oneof a pairof spaced shoulders formed on said latch wheel, according to the direction of rotation'of said driving shaft, pend ing storage of agiven amount of energy in said torsion spring, the edge portion of said star wheel underlying each of said pawls;whereby upon a'given-degree of positive movementof said star wheel by said driving shaft the active pawl is lifted f-rom' locking" engagement .with the co:

operating shoulder on said latch wheel to permit r a' predetermineddegree of rotary'movement of :j.

I the latter underthe bias of said; torsionspring,

and said driven shaft having circuitcontrolling elements associated therewith.

corresponding In like manner it is V 3. In an operatin mechanism for a circuit controller, combination, rotatably -"mounted driving and driven shafts arranged in axial alinement, means including a coiled torsion spring interposed between said shafts for" effecting rotation of said drivenshaft from each of a plurality of positions'thereof to anotherysaid last mentioned means comprising a latch wheel fixed to said driven shaft, a pair of pivoted pawls having spring-biasing means common thereto, said pawls being selectively cooperable with said latch wheel to' temporarily lock the same pending storage of a predetermined amount of energy in; said torsion sprlng, astar wheel rotatably supported by said driving shaft, a pin carried by said driving shaft and having a predetermined degree of lost motion with respect to said star wheel, a second pin carried by said latch wheel and also having a predetermined degree of lost motion with respect to said star wheel, said torsion spring having integral extensions arranged on opposite sides of each of said pins and normally acting to maintain said wheels in a given rotar relationship to each other, said star wheel coacting with said pawls selectively, according to the direction of rotation of said driving shaft, to effect disengagement of the pawl from said latch wheel, whereby the energy stored in said torsion spring-is released to effect movement of said driven shaft to its next succeeding position with a snap action, and the other pawl under such conditions cooperating with said latch wheel to positively limit the angular degree of rotary movement of said driven shaft.

4. In an operating mechanism for a circuit controller, in combination, rotatably mounted driving and driven shafts arranged in axial alinement, means including a coiled torsion spring interposed between said shafts for effecting rotation of said driven shaft from each of a plurality of positions thereof to another, said last mentioned means comprising a latch wheel fixed to said driven shaft, a pair of pivoted pawls having spring-biasing means common thereto, said pawls being selectively cooperable with said latch wheel to temporarily lock the same pending storage of a predetermined amount of energy in said torsion spring, a star wheel rotatably supported by said driving shaft, a pin carried by said driving shaft and having a predetermined degree of st motion with respect to said star wheel, a second pin carried by said latch wheel and also hav ing a predetermined degree of lost motion with respect to said star wheel, said torsion spring having integral extensions arranged on opposite sides of each of said pins and normally acting to maintain said wheels in a given rotary relationship to each other, said star wheel coacting with said pawls selectively, according to the direction of rotation of said driving shaft, to effect disengagement of the pawl from said latch wheel, whereb the energy stored in said torsion spring is released to effect movement of said driven shaft to its next succeeding position with a snap action, the other pawl under such conditions cooperating with said 1atch wheel to positively limit the angular degree of rotary movement of said driven shaft, and the spring-biasing means common to said pawls acting to return the same to their normal positions relatively to each other and to said star wheel and latch wheel after each snap movement of said driven shaft.

5. In an operating mechanism for a circuit controller, in combination, rotatably mounted driving and driven shafts arranged in axial aline- 10 ment, means including a coiled torsion spring interposed between said shafts for effecting rotation of saiddriven shaft from each of a plural- 'ity of positions thereof to another, said last mentioned means comprising a latch wheel fixedto 'said'driven shaft, a-pair of pivoted pawls having spring-biasing meanscommon thereto, said pawl-s being selectivelycooperable with said latch wheel to temporarily lock the same pending, storage of ap-redetermined amount of energy in said torsion spring, a star wheel rotatably supported by said driving shaft, 2. pin carried by said driving shaft and havinga predetermined degree of lost motion with respect to said 'star wheel, a second pin carried by said latch wheel and also having a predetermined degree of lost motion with respect to said star wheel, saidtorsion springhaving integral extensions arranged on opposite sides of each of said pins and normally acting to maintain said wheels in a given rotary relationship to each other, said star wheel c'oa'cting with said pawlsselectively, according to the direction 'of rotation of said driving shaft, to efiect disengagement of the pawl from said latch wheel, whereby the energy stored in said torsion spring is released to effect movement of said driven shaft to its next succeeding position with a snap action, the other pawl under such conditions cooperating with said latch wheel to positively limit the angular degree of rotary movement of said driven shaft, the spring-biasing means common to said pawls acting to return the same to their normal positions relatively to each other and to said star wheel and latch wheel after ach snap movement of said driven shaft, and said last mentioned spring-biasing means also acting, in the event of failure of said torsion spring, to permit forcible movement of said star wheel and said latch wheel relatively to either or both of said pawls, for the purpose set forth.

6. In a reversing snap action operating mechanism for a drum controller, in combination, rotatable driving and driven shafts arranged in axial alinement, means adapted upon a predetermined degree of rotary movement of said driving shaft in either direction to effect a corresponding degree of rotary movement of said driven shaft with a snap action, said means comprising a latch wheel rigidly attached to said driven shaft, a star wheel carried by said driving shaft and rotatable with respect thereto, said star wheel having an opening formed therein eccentric to the axis thereof, a pin attached to said latch wheel and extending with a predetermined amount of clearance through said star wheel opening, a second pin attached to and movable with said driving shaft in an arc parallel to said first mentioned pin, a coiled torsion spring surrounding said driving shaft and having end portions arranged to overlap opposite sides of said pins, means affording a lost motion driving connection between said second mentioned pin and said star wheel, means comprisin a pair of hook-shaped pawls normally spring-biased to a given relationship to each other and to said latch wheel, said pawls acting selectively to temporarily lock said latch wheel against rotation in either direction pending storage of a given amount of energy in said torsion spring, and said star wheel acting in each instance to effect releasing movement of the active pawl, whereby said latch wheel and said driven shaft are moved with a snap action to the next succeeding position thereof, the other pawl acting in each instanceto positively limit the degree of said movement last mentioned. a

7. In a reversing snap action operating mech- 1 anism for a drum controller, in combination, ro-

tatable driving and driven shafts arranged in axial alinement, means adapted upon a predetermined degree of rotary movement of said driving shaft in either direction to effect a corresponding degree. of rotary movement of said driven shaft with a snap action, said means comprising a latch wheel rigidly attached to said a driven shaft, a star wheel carried by said driving nection between said second mentioned pin and 7 said star wheel, means comprising a pair of hookshaped pawls normally spring-biased to a given relationship to each other and to said latch wheel, said pawls acting selectively to temporarily lock said latch Wheel against rotation in either direction pending storage of a given amount of energy in said torsion spri said star wheel act- 7 ing in each instance to efiect releasing movement of the active pawl, whereby said latch wheel and said'driven shaft are moved with a snap action to the next succeedin position thereof, the other pawl acting in each instance to positively limit the degree-of said movement last mentioned, and the spring-biasing means associated with said pawls serving to prevent binding of said pawl's with respect to said star wheel and said latch wheel in the event of failure of said torsion spring} to thereby render effective the aforementioned meansaffording a positive driving connection between said driving and driven shafts.

CHRISTIAN E. BUERKI. v HAROLD Ly. MEKELBURG.

REFERENCES CITED' The following references are of record in the file'of this patent:

' UNIT D STATES PATENTS Date Number Name 7 7 660,634 Guett Oct. 30; 1900 2,009,383 Blume July 30, 1935 2,395,969 Kaser Mar. 5, 1946 1,514,013 Rudolph Nov. 4, 1924 334,173 Kaiser -1 Jan. 12, 1886 Huhn June 30,1936 

